Key Strata Research Articles

Determination of caved and water-conducting fractured zones of “two soft and one hard” unstable coal seam

The height of the development of a caved zone (CZ) and a water-conducting fractured zone (WCFZ), hereinafter “CZ and WCFZ”, in mining of soft coal with a soft mine floor, hard mine roof and different thicknesses of the coal seam, hereinafter “two soft and one hard” unstable coal seam, is of interest in the long wall coal mining. An observation borehole was drilled above a coal seam with an average thickness of 4.0 m. By using borehole imagery technique and comparing the borehole images at different distances from the working face, the height of “CZ and WCFZ” at the working face is calculated under the condition of insufficient mining. Based on field observations, a 3D numerical model is developed under the condition of full mining, the height of CZ is calculated to be 14.4 m and the height of WCFZ calculated to be 67.0 m. The numerical model also shows changes in the vertical stresses in the overburden strata above the roof of the coal seams and it is related to the development of the “CZ and WCFZ”. At the same time, based on the key strata theory and multiple linear regression, the height of WCFZ in the working face of this case study is predicted to be 67.0 m and 64.8 m respectively, which is close to the numerical simulation results. At the same time, 30 groups of measured data are collected to analyze the main factors affecting the WCFZ, and the influence of different lithology characteristics of overburden strata on the WCFZ is mainly discussed. The results show that the height of WCFZ is hard–hard > hard–soft > soft–hard. The results provide important practical guidelines for the prevention and control of roof water hazards in coal mine thus improving the safety of mining.

Dynamic loading induced by the instability of voussoir beam structure during mining below the slope

Dynamic loading events in the longwall faces under slopes in the Shendong Coalfield, China, seriously limit the safety and efficiency of mining. The slope characteristics, such as direction, height, and angle, determine the load type and the stability of the voussoir beam structure (VBS) formed by fractured blocks of the primary key stratum (PKS). Whether or not dynamic loading events will occur can be directly determined based on the presence or absence of a stable VBS in the PKS. Based on this relationship, six structural mechanical VBS models for different load distributions were established and then the effects of the slope direction, height, and angle on the stability of VBS was analysed. Changes of load type intensified the compression force between the hinged blocks. When the compression force between blocks exceeded the strength of the rock, VBS instability and dynamic loading events occurred. The compression force in the VBS increased with increasing slope angle and height when the slope directions were similar, becoming more pronounced for mining under the uphill sections of the slopes. Therefore, a method of determining the critical slope parameter values indicating a risk of dynamic loading was proposed, enabling such slopes to be recognised in advance. Measures such as slope top cutting or backfilling can then be applied to prevent potential dynamic loading accidents. This study can provide guidelines for safe mining under geological conditions involving widespread slopes and gullies.

Study of the Stability Control of Rock Surrounding Longwall Recovery Roadways in Shallow Seams

The rock pressure appearance of longwall faces in shallow seams is generally violent, and roofs and supports are susceptible to damage during equipment extraction. Stability control of the rock surrounding longwall recovery roadways allows safe and rapid equipment extraction. Herein, via theoretical analysis, numerical simulations, and field observations, the stability control of the rock surrounding recovery roadways is studied to ensure the release of the accumulated rock pressure on the roof, the working resistance of the supports and the reasonableness of the recovery roadway support design. Pressure-relief technology is introduced to release the accumulated rock pressure before equipment extraction, and a discriminative approach is proposed to determine the breaking and articulated forms of key strata and broken blocks, respectively. On this basis, mechanical models of roof instability are established based on four key stratum structures in the overburden of shallow seams. Methods for calculating a reasonable working resistance for supports are discussed. Finally, Liangshuijing Coal Mine and Fengjiata Coal Mine are taken as research objects to evaluate the roof stability of recovery roadways based on observations of weighting characteristics. The support working resistances and reasonable recovery roadway widths under three key stratum structures are determined. Considering the time effect of plastic zone development, the support design of recovery roadways is optimized. FLAC2D software simulates the surrounding rock control effect of two support designs, and roof subsidence curves are obtained. The results show that the key to equipment extraction in shallow seams is to ensure that supports have reasonable working resistances and to improve the support of recovery roadways. The results provide a reference for the selection and extraction of supports in shallow seam faces.

Structural Characteristics of the Overlying Strata in a Fully Mechanized Longwall Face with the Low-Position Thick-Hard Roof

Strata activity is enhanced in the condition of the thick seam and large mining height, which increases the difficulties in roof management. A detailed understanding of roof structure characteristics and its movement law is a key to control the strata behavior. Since the existing formula hardly applies to some specific cases of geological conditions, such as the condition of a fully-mechanized longwall face with the low-position thick-hard roof in Suancigou Mine, a new formula of distinguishing structural characteristics of key strata based on a mechanical model of rock beam in periodic motion was proposed. Considering the relationship between the allowed rotating space of key strata and its limited rotation, the judgment criterion whether a cantilever beam can be formed was established. Also, a method for calculating the reasonable working resistance of hydraulic supports under these special roof structure was deduced from the angle of preventing rotating instability of the main roof. A field application was performed at 6-105-2 working face, and the proposed judgment criterion indicated that the LPTHR would break in the form of a voussoir beam structure at the Z1 drilling area, while at Z2 and Z3 drilling area, the broken LPTHR would behave as the cantilever structures. Field monitoring results showed that the limit-rotation-based cantilever structure criterion could accurately discriminate the structural characteristics of LPTHR. According to the calculation formula of support resistance of hydraulic support, the reasonable working resistance of hydraulic supports in 6-105-2 working face was determined to be 16,245 kN.

Sensitivity analysis of overburden water-resistant strata stability based on the mechanical properties of backfill body

Strata movement control during coal seam’s backfill mining is very much related to the mechanical properties of backfill body in goaf. A mechanical model of the structural water-resistant strata (SWRS) of stope overburden in backfill water-preserved mining (BWPM) was established on the basis of the key strata theory in ground control. This approach was conducted to investigate the mechanical properties of backfill body on the overburden water-resistant strata stability. The proposed model was based on the compressive mechanical properties of the filled gangue, which considered the linear and nonlinear elastic mechanical properties of backfill body. The stability mechanics criterion of the SWRS of stope overburden in BWPM on the nonlinear elastic foundation was deduced by introducing the tensile yield criterion. The maximum tensile stress (MTS) that acts on the SWRS of stope overburden decreased with the increase of the backfill body’s linear elastic foundation coefficient of k1 and the nonlinear elastic foundation coefficients of k2 and k3. However, the MTS rapidly decreased with the increase of k1 and slowly decreased with the increase of k2 and k3. The sensitivity analysis indicated that k1 exhibited the greatest effect on the MTS that acts on the SWRS, thereby accounting for 72.38%. In addition, k2 and k3 showed less effect on the MTS that acts on the SWRS, thereby only accounting for 19.56% and 8.06%, respectively. Results showed that the backfill body’s linear elastic foundation coefficient plays a very important role in controlling the stability of the SWRS of stope overburden in BWPM. Increasing k1 is more beneficial to the stability control of the water-resistant strata of stope overburden than increasing k2 and k3, especially the latter.

Analysis of main factors influencing the apertures of mining-induced horizontal fractures at longwall coal mining

Main factors influencing the wide range of apertures (from 50 to 400 mm) of mining-induced horizontal fractures (Torezko-Snezhnyanskaya coal area, Ukraine) at traditional (without grout injection into bed separation) longwall coal mining were analysed. Apertures of these fractures were directly measured (using an original experimental device) in vertical boreholes drilled from ground surface to active underground coal workings. It is revealed that main factors influencing the apertures of mining-induced horizontal fractures are thickness of extracted coal seam, distance from extracted coal seam to horizontal fracture, uniaxial compressive strengths of rock layers above and below the fracture, thicknesses of rock layers above and below the fracture, and thickness of “layer-bridge” (key strata). It is argued that influence of above-mentioned factors on the aperture is strongly dependent on combinations (Cases 1–5) of values of these factors. The mathematical forms of correlations (and values of involved empirical coefficients) and role (dominant or insignificant) of each factor in each of five Cases are discussed.

Study of the Dynamic Development Law of Overburden Breakage on Mining Faces

Based on the geological conditions of overburden rock, the dynamic development law of overburden breakage was investigated by theoretical analysis and similarity model experiments in this paper. The formula of the compressive strength and No. ratio was obtained by testing the compressive strength of cylinder samples of similar materials. It can be seen from the overburden fracture evolution model established by theoretical calculations and similarity model experiments that the overlying rock layer’s breakage law is consistent. Additionally, the height of the “three zones” and the law of the fracture angle are basically consistent. Obtaining the synchronous collapse of the overlying strata controlled by the key strata, the interval of the upper key strata is larger than that of the lower key strata, and the mining interval is approximately double the size of the deformed rock height. According to the overburden movement, the distribution law of the overburden separation rate is obtained. The strain in the stress concentration area is negative, and when the stress is released suddenly, the strain increases rapidly. Fracture development is detected by the p-wave velocity in the model. Moreover, certain guidance for the horizon selection of high and low-level gas drainage roadways is provided by this study.

Study on the structural forms of the key strata in the overburden of a stope during periodic weighting and the reasonable working resistance of the support

AbstractMany mines often passively select supports with a higher yield load to avoid the occurrence of support crushing and roof falling during periodic weighting. This method is not conducive to improving production efficiency or reducing mining costs, but it can ensure safe mining. An effective method for overcoming these problems is to determine the reasonable working resistance of the support according to the structural forms of the key strata in the overburden of the stope during periodic weighting. In this paper, comprehensive theoretical analysis, numerical simulation, and field observation were applied to study the discrimination of the key stratum structure (KSS) during periodic weighting and the calculation method of the support load. First, the KSS that affects the periodic weighting of the stope was classified. The “twice discrimination method” was proposed for determining the breaking form of the key strata and the articulated form of the broken blocks. On this basis, the spacing condition that determines whether adjacent key strata interact was analyzed. The discriminant conditions for synergistic breaking between the first subordinate key stratum (SKS1) and the upper key stratum were derived for the cases in which the SKS1 periodically breaks in the form of a cantilever beam, a voussoir beam, and a step beam. These conditions provide the basis for distinguishing the KSS in the overburden of the stope. In addition, mechanical models of the roof structure during periodic weighting were established, and general formulas for calculating the support loads of stopes with a single‐key‐stratum influence structure and a multikey‐stratum influence structure were presented. Finally, five fully mechanized coal faces with various mining conditions in China were considered for engineering verification. The results of this study demonstrate that the proposed method for determining the reasonable working resistance of the support is consistent with the field practice. The research results can provide a reference for roof control and support selection of stopes.

Grouting of bed separation spaces to control sliding of the high-located main key stratum during longwall mining

The gob-side entry 150 – 180 m behind the 14201 working face at Majialiang coal mine is severely deformed. We developed a new technique to control the behaviour of the high-located main key stratum (HMKS) to improve mine safety. The failure type and breaking span of the HMKS were determined based on key stratum theory and the voussoir beam model. By monitoring the deformation of the entry and surface subsidence, we found that the main cause of the large deformation of the gob-side entry was sliding of the HMKS. A new technique is proposed to add grout between the separated beds during mining. Physical simulations indicated that this technique is efficient in controlling sliding of the HMKS and avoiding strong dynamic loading, with the peak abutment stress reduced by 59%. Grouting stations were set up at a spacing of 150 m behind the advancing work face based on the principles and key parameters of the technique and the geological conditions at Majialiang coal mine. Before the HMKS began to slide, we injected high-water content materials with a water to cement ratio of 1.5:1 into the bed separation space to prevent breaking of the key strata.

Mechanism of Water Inrush and Controlling Techniques for Fault-Traversing Roadways with Floor Heave Above Highly Confined Aquifers

Floor heave and water inrush accidents are likely in fault-traversing roadways above highly confined aquifers. In this paper, the deflection curve equation for the key floor stratum of a fault-traversing roadway in the Zhaogu no. 2 coal mine was derived based on the cantilever beam model, and the line strain in the failure zone, e, was introduced to characterize the relationship between floor heave and deformation of deep intact rock layers. Then, three- dimensional pre-grouting technology was established for floor reinforcement. Analysis indicated that the rock surrounding the fault-traversing roadway was highly fractured, increasing the risk of water hazards. Numerical UDEC simulations showed that the plastic zone of the roadway was greater due to the faults; the floor heave, in this case, was 2.6 times greater than without faults. However, water pressure applied to the floor had a limited impact on deformation of the surrounding rock. The measured maximum deflection of the stratum was 644 mm, and the line strain e in the failure zone in the floor was 67 mm, which resulted in a difference of 3.5% compared with the modelled results. The apparent resistivity in the grouted areas, observed through comprehensive geophysical explorations, was increased, suggesting that the grouting reinforcement had been successful.

Key Strata Identification of Overburden Based on Magnetotelluric Detection: A Case Study

The severe overburden failure induced by high-intensity mining is the essence of eco-environmental problems in Northwest China, and the degree of overburden failure is closely related to the location and failure of key strata (KS), which controls part of the strata in the overburden. In order to solve the problems of traditional KS based on mechanical parameters and numerical simulation methods that are time consuming, complex, expensive, and work intensive, it is necessary to find a simple and fast KS identification method. Based on the KS theory, which has been successfully applied in the field practice for nearly 30 years, and its current identification method by calculation or software, the magnetotelluric (MT) detection method was selected. According to the principle of MT detection method, the main influencing factors were analyzed. By summing up the relationship between the geological characteristics of the KS and its apparent resistivity (AR), the AR trends of ten kinds of lithology are given, and the identification mechanism of the MT detection method is revealed. Through the field measurement in Daliuta coalmine and the accuracy verification by the theory calculation, the KS obtained by the two methods are consistent. The results show that the MT detection method can be used to quickly identify the KS, and it is simple, convenient, and fast. It provides a reference for optimizing mining technology, mine pressure control, and mine precision.

Study on rockburst prevention technology of isolated working face with thick-hard roof

Based on the literature statistical method, the paper publication status of the isolated working face and the distribution of the rockburst coal mine were obtained. The numerical simulation method is used to study the stress distribution law of working face under different mining range. In addition, based on the similar material simulation test, the overlying strata failure modes and the deformation characteristics of coal pillars during the mining process of the isolated working face with thick-hard key strata are analyzed. The research shows that, under the influence of the key strata, the overlying strata formation above the isolated working face is a long arm T-type spatial structure. With the mining of the isolated working face, a series of damages occur in the coal pillars, causing the key strata to break and inducing the rockburst occurs. Combined with the mechanism of rockburst induced by the dynamic and static combined load, the source of dynamic and static load on the isolated working face is analyzed, and the rockburst monitoring methods and the prevention and control measures are proposed. Through the above research, the occurrence probability of rockburst can be effectively reduced, which is of great significance for the safe mining of deep coal mines.

The Key Stratum Structure Morphology of Longwall Mechanized Top Coal Caving Mining in Extra‐Thick Coal Seams: A Typical Case Study

Longwall mechanized top coal caving mining (LMTCCM) in extra‐thick coal seams has its own characteristics. The law of mining pressure and overlying strata failure height in extra‐thick coal seams are much larger than those of medium‐thick and thick coal seams. The key stratum structure morphology also has an important influence on the law of overlying strata movement and stability of surrounding rock. Based on the engineering geological conditions, this paper used the method of theoretical analysis and numerical simulation to study the key stratum structure morphology of LMTCCM in extra‐thick coal seams. The results show that under the condition of LMTCCM in extra‐thick coal seams, the key stratum forms the structure of low cantilever beam and high hinged rock beam. With the increase of coal seam thickness, the breaking position of cantilever beam is closer to the coal wall. Through theoretical calculation, it is obtained that the breaking length of cantilever beam is 31.5 m and the breaking position of cantilever beam is 15.4 m away from coal wall. With the increase of cycle, key strata will undergo the evolution law from the generation of longitudinal cracks to the hinged structure and then to the cantilever beam structure. The breakage of key strata will cause the expansion of longitudinal cracks and the overall synchronous movement of overlying strata. With the increase of coal seam thickness, the distribution of longitudinal cracks will gradually transfer from the upper part of goaf to the deep part of coal body in space and increase in quantity. This research is of great significance for improving the stability of overlying strata and ensuring the safe and efficient mining of extra‐thick coal seams.

Key Stratum Structure and Support Working Resistance of Longwall Face with Large Mining Height in the Shallow Coal Seams, China

The fully mechanized mining with large mining height is the main method for high yield and efficient coal mining in China. The key stratum structure (KSS) is the basis of revealing the mechanism of roof weighting and determination of support working resistance of the longwall face with large mining height (LFLMH) in the shallow coal seam. The height of the caving zone at LFLMH is large, the thick immediate roof forms the “short cantilever beam” structure commonly, and the hinge layer of the overlying key stratum will move upward to the higher position. The “high position oblique step voussoir beam” structure of single‐key stratum (SKS) and “oblique step voussoir beam and voussoir beam” structure of double‐key stratum (DKS) in the shallow coal seam were proposed with physical simulation and Universal Distinct Element Code (UDEC). The analysis of the KSS and numerical simulation reveals the mechanism of strong roof weighting at the SKS longwall face and large‐small alternate periodic weighting at the DKS longwall. It is concluded that the large static load caused by the “equivalent immediate roof (EIR)” is the basic load, and the instability load of the KSS is the additional dynamic load of support. Besides, the calculation methods of the reasonable support working resistance at LFLMH were obtained and verified with engineering applications.

Research on Surface Failure Law of Working Faces in Large Mining Height and Shallow Buried Coal Seam

In the process of high‐intensity and large‐space mining in Shendong mining area, various surface cracks are generated on the surface, resulting in serious damage to the surface buildings and the local ecological environment. To study the influence of overlying rock movement on surface failure of near‐field single key strata of near‐shallow buried and large mining height working face, the relationship between overburden movement, strata pressure appearance, and surface failure at working face 52307 in Daliuta mining area was analyzed by field measurement and numerical simulation. The results show the following: (1) there is only one thick and hard key stratum in the overburden of large mining height and near‐shallow buried working face. Under the condition of presplitting roof blasting, the first weighting step is still as high as 95 m, and the periodic breaking step of roof is 20–30 m. During the weighting, the working resistance of support is still close to the rated resistance. (2) The single key stratum plays an obvious role in controlling overburden movement. After the first weighting of the working face, a stepped subsidence crack appears on the surface within a short time, and the crack lags behind the working face for about 5 m. (3) During each periodic weighting process, the breaking and subsidence of key blocks are accompanied by surface cracks.

Deformation Rules for Surrounding Rock in Directional Weakening of End Roofs of Thin Bedrocks and Ultrathick Seams

With the deployment of China’s energy strategy in the western regions, complex geological mining conditions such as thin bedrock and ultrathick seams in western China have caused a series of problems such as serious deformation of the surrounding rock at the ends of the working face and the increase in the lead abutment pressure of the roadways; the research on end roof deformation in the resource exploitation in western China has become one of the great demands of the industry. Based on the failure characteristics of rock mass, relying on the actual mining geological conditions of a coal mine in Inner Mongolia, the failure characteristics of the overlying rock strata under the influence of mining were simulated and analyzed using similar material simulation experiment, which intuitively reproduced the failure and deformation processes of the immediate roof, main roof, and key strata and revealed the mechanical mechanism of the directional weakening of the end roof. It is of great significance for the stability control of the surrounding rock at the end of the fully mechanized caving face in the thin bedrocks and ultrathick seams, reducing the abutment pressure of gate roadway and controlling the spontaneous combustion of residual coal in the goaf.

Study on the Evolution Law of Fracture Field in Full‐Mechanized Caving Mining of Double System and Extrathick Coal Seam

During the full‐mechanized caving mining, the overburden strata in the double system and extrathick coal seam of the Datong mining area are largely damaged. Water and harmful gas in the old goaf may be discharged when overburden fractures evolve to the upper goaf, which poses a major threat to the normal production of the panel. To study the movement of overburden strata and the evolution of fracture field under the full‐mechanized caving mining of the double system and extrathick coal seam, panel 8309 of Tongxin mine was taken as the research object; the evolution rule of fracture field in the full‐mechanized caving mining of the double system and extrathick coal seam was obtained through field measurement and physical similar simulation. The results show the following: (1) the far‐field and near‐field key strata play a decisive role in controlling the fracture evolution of overburden strata. When the far‐field key strata break and the development height of fractures reaches 220.9 m, panel 8309 is connected with the overburden goaf. (2) Based on the “O‐shape circle” theory of mining fracture, with the continuous advance of the panel, the overburden breaks periodically, and a “fracture surface” with a certain angle of 61°–67° can be formed along with the advancing direction of the panel. (3) When the key strata are broken and the development height of fractures reaches the maximum, the fracture surface is formed as the “main fracture surface,” which is the only downward discharge pathway for goaf water and harmful gas. The overall shape fracture surface is “inverted trapezoid” in the upper part and “positive trapezoid” in the lower part. (4) Based on the field measurement of the water level of borehole and the observation of mine pressure, the correctness of the evolution law of the similar simulated fracture field is verified.

Sliding instability characteristics and re-stabilization mechanism of key stratum in thin-topsoil SCS mining: a computer-aided case study from the Niushan Coal Mine, China

Roof step subsidence and support crushing accidents caused by the sliding instability of fractured single key stratum often occur in shallow coal seam (SCS). For this reason, the exploration of fracture displacement laws and control mechanism of key stratum in thin-topsoil SCS is of great significance for both roof control and safety production. From this perspective, in this study, numerical simulation and theoretical analysis were conducted to establish a mechanical model of the key stratum structure after sliding instability in thin-topsoil SCS. Moreover, its instability characteristics and re-stabilization control mechanism were analyzed. The results revealed that the fractured key stratum block could reach re-stabilization without any support crushing after sliding instability in thin-topsoil SCS depending on the significant unloading effect of the topsoil. The mechanical model of the key stratum structure after sliding instability was also analyzed to obtain the criterion for the re-stabilization of the sliding instable rock block. The computational analysis corroborated that increasing the support intensity could promote the re-stabilization of fractured key stratum block after sliding instability, and the required support working resistance could be obtained for preventing support crushing incidents.

Directional Blasting Fracturing Technology for the Stability Control of Key Strata in Deep Thick Coal Mining

Under the conditions of high ground stress and mining disturbance, the strata breakage that is induced by mining is severe. Thus, it is critical to investigate the structural characteristics of key strata (KS) in deep thick mining. This study introduces an innovative technology, namely, directional blasting fracturing, in which an energy-gathering tube is installed in a borehole and an explosive is detonated to break the roof in a specified direction. A theory of balanced bulk filling is established based on the requirements of developing a voussoir beam structure, which can be used to effectively evaluate the percentage of bulk filling in gob and to determine to which structure the key strata belongs. Based on this theory, two types of novel structural models in the advancing and lateral directions of the longwall face are established and defined for studying the roof fracturing mechanism. Compared with a cantilever structure, Model C can develop a stable voussoir beam structure, limiting the rotation space of the KS and reducing both the peak abutment pressure and the dynamic disturbance time in the advancing of the longwall face. Model E is defined as when the technology of directional blasting fracturing effectively cuts a stress transfer path into the barrier pillar. The peak abutment pressures on the barrier pillar and auxiliary entry are smaller, and the dynamic disturbance time is shorter, which can effectively improve the stability of the auxiliary entry. The key parameters of directional blasting fracturing are designed and constructed, and they include the roof fracturing height, angle, and charge structure. The field application performance of this innovative technology at the longwall face of 3−1101 in Hongqinghe coal mine was evaluated by analyzing the chock pressure stress, the pillar pressure stress, and the deformation of the auxiliary entry during mining, which lays a foundation for the application of this technology in coal mines in China.

A new theoretical method for calculating front abutment stress during coal mining

AbstractThe calculation of abutment stress has always been the most important topic in safe underground mining and design. In this paper, based on the formation mechanism of abutment stress, combined with the mechanical properties of actual strata and the theory of elastic foundation beams, a structure model of overlying strata with an elastic foundation is established, and a new theoretical calculation method of abutment stress is proposed. The new calculation method takes into account the interaction of the overlying key strata and the effect on the transmission of the front abutment stress and then analyzes the stress patterns of multilayered key strata under the combined action of the bending moment, shear force, and nonuniform load and its transmission to the underlying strata. In addition, based on field observations of panel 10 305 in the Xinglongzhuang coalmine, the influence range, peak position, and variation trend of the front abutment stress before and after breaking of the overlying key strata are studied and verified. The results show that the influence range of the abutment stress remains unchanged after KS1 breaks (eg, from 0 to 180 m), and its peak position shifts forward from 8 to 19 m, while the influence range (0‐180 m) and its peak position (6‐8 m in front of coal wall) remain unchanged after KS2 breaks; the abutment stress decreases, and the maximum decrease is 3.9 MPa in the range of 0‐22 m ahead of the coal wall after KS1 breaks, while the maximum decrease in the abutment stress is 2.1 MPa in the range of 0‐71 m ahead of the coal wall after KS2 breaks. The results of the new calculation method are basically consistent with the field observations and the existing theoretical results, showing that the method has good adaptability and reliability and can provide a new theoretical basis for on‐site design and construction practices.